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Boulder researchers study fate of oil in Gulf spill

Airborne measurements allow estimate of spill's rate

By Laura Snider Camera Staff Writer

Posted:
03/14/2011 07:41:42 PM MDT

Updated:
03/14/2011 07:42:10 PM MDT

As an oily mixture of gases and fluids gushed from the broken Macondo well into the Gulf of Mexico last June, Boulder scientists flew a high-tech research plane over the water to better understand the amount -- and ultimate fate -- of the leaking hydrocarbons.

The results of the scientific mission -- led by researchers at the National Oceanic and Atmospheric Administration -- have been accepted for publication by the journal Geophysical Research Letters.

"This veritable flying chemistry laboratory was jam-packed with all necessary sensors," said A.R. Ravishankara, director of the Chemical Sciences Division at NOAA's Earth System Research Laboratory in Boulder. "It allowed for a very careful look at what was getting into the air from the oil spill."

Oil began streaming into the Gulf last year from a well owned by British Petroleum after an explosion rocked the Deepwater Horizon drilling rig on April 20. An estimated 5 million barrels of oil spilled from BP's well over 86 days until the well was capped in July.

The data collected by NOAA's WP-3D research plane -- which was, serendipitously, already loaded with the appropriate equipment for planned research flights in California -- helped scientists understand what was happening to the individual components of the oily concoction.

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Researchers already knew the relative chemical makeup of the reservoir tapped by the Macondo well, which includes a variety of hydrocarbons such as methane, benzene and ethane. So when the instruments on board the plane failed to measure any concentrations of methane in the atmosphere, for example, researchers could conclude that the methane must have dissolved entirely in the water column before reaching the surface. Scientists also learned that only small portions of the benzene, a known carcinogen, and ethane in the oil mixture escaped into the atmosphere, meaning those compounds were also largely dissolved into the Gulf.

"Whether a given compound of this complicated mixture dissolves or whether it evaporates tells us where it ends up in the marine environment," said NOAA scientist Tom Ryerson, lead author of the study.

In all, Ryerson and his team found that about one-third of the chemical compounds dissolved in the water on their way to the surface. Fourteen percent evaporated quickly after reaching the surface, and another 10 percent evaporated more slowly, after a day or so.

Measuring the quantities of compounds that evaporated into the atmosphere also allowed scientists to calculate a minimum amount of the oil mixture spilling into the ocean per day, which they say was about 32,600 to 47,700 barrels on June 10.

The true amount, however, could be higher since the aircraft could not measure compounds that did not travel to the surface.

"In the airborne measurements we miss one potentially key fraction of the total, and that's the portion not surfacing," Ryerson said. "We're blind to that."

Ryerson and his colleagues are now working with scientists who study the chemistry within the water column to get a more complete picture of where all of the spilled components end up.

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